Silicon carbide (SiC) is an advanced material typically used in power electronics, as it is a wide band gap semiconductor (Eg=3.26 eV) with a low intrinsic carrier concentration (ni=5×10−9 cm−3), high electric field of breakdown (Eb=2.2 MV/cm), and high thermal conductivity (κ=3.0-3.8 W/cm-K). Furthermore, SiC is the only wide band gap semiconductor that has silicon dioxide (SiO2) as a native oxide. Due in part to these advantageous properties, SiC has been used in power semiconductor devices, such as Schottky diodes and metal-oxide-semiconductor field-effect transistors (MOSFETs), for automobiles, power converters, defense applications, and other systems.
SiC MOSFETs have historically been plagued by very low carrier mobility in the inversion channel, resulting from a high density of interface traps at the SiC/SiO2 interface. Significant progress has been made with respect to interface passivation over the last decade. In particular, nitric oxide (NO) post-oxidation annealing has been shown to provide an acceptable channel mobility of around 35 cm2/V-s in SiC MOSFETs. However, this value is only about 4% of the bulk mobility of 4H-SiC (which is about 800-1000 cm2/V-s). As such, the channel resistance (which is inversely proportional to the inversion channel carrier mobility) in state-of-the-art 4H-SiC power MOSFETs still contributes to about half the total conduction loss.
Recent research has indicated that phosphorus passivation (P-passivation) of a SiC/SiO2 interface is more effective than NO passivation, providing peak mobilities of 80-90 cm2/V-s. However after typical P-passivation, the oxide is no longer SiO2 but, rather, is transformed to phosphosilicate glass (PSG). In MOSFETs including an insulation layer of PSG, the polar characteristics of the PSG will typically cause threshold voltage instabilities, rendering the MOSFETs unstable and of little or no practical use.